The invention relates to a process and an apparatus for the production of high-tenacity, technical-grade yarns, particularly of polyamide and polyester, by spin-drawing, in which the filaments extruded from a spinneret are cooled in a cooling zone by being expressed to a tranversely directed stream of air, are passed over a preparation device and then passed directly over several sets or systems of rolls, of which the first set consists of feed rolls. The continuous filament yarn, which forms a draw point, is drawn in at least one draw field, between at least two roll systems, of which the one following the draw field is a draw roll system. The yarn is subjected to a temperature of at least 160.degree. C. in at least one roll system, and is finally passed over a set of let down rolls before it is wound up at a speed of at least 2,200 meters/min.
Technical-grade yarns are required to have specific properties, in particular a high tenacity, a low break elongation and a low incidence of yarn defects in the feed yarn. These requirements are technologically interrelated with high draw ratios in the production of feed yarn. Higher draw ratios, however, are limited where the continuous filament yarn has already been damaged by the drawing operation and breakage occurs. This limit is reached considerably earlier at high production speeds. The technical and economic merit of the spin-draw process at high-speed production can, however, be rated as positive only if, at the same time, the textile performance of the yarn is not impaired, and even improved.
From German published patent application DE-OS No. 1,435,467, a process for spin-drawing of polyester at speeds of 1,000 to 4,000 m/min. is known. The process disclosed therein utilizes a thermal treatment of the filaments at certain periods of residence time prior to drawing, the heating being effected on or between conical pins. The mechanical system used in the process is technically complicated and of little use since, for reasons of productivity, at least two continuous filament strands are to be processed on the pins.
U.S. Pat. No. 3,452,131 discloses a process for drawing polyamide filaments in which the filament yarn is orientation drawn in two stages and the yarn is additionally heated in the first stage by a gaseous medium.
German published patent application No. 1,912,299 discloses a spin-drawing process, in which a water deficient finish is applied to the filament and the drawing is effected in at least two stages, with the draw ratio of the first stage being between 1.15 and 3.0. The use of a snubbing pin, specified in the application, at high production speeds leads to a high amount of friction and hence to an uncontrollable increase in the temperature of the pin.
U.S. Pat. No. 4,003,974 discloses a process for spin-drawing of polyester. As an additional expedient in the drawing operation, a steam jet for heating the yarn to a temperature of 75.degree.-250.degree. C. is employed. Drawing is effected in a field between two sets of rolls.
Processes for spin-drawing of polyester are known from U.S. Pat. Nos. 3,790,995 and 3,715,421, in which the feed and draw rolls are provided with a certain surface roughness to allow a slippage of the filaments on both sets of rolls. However, it was found that, at higher production speeds, the filament slippage produced a high degree of friction and the frictional heat thus generated caused an uncontrollable increase in the temperature of the rolls.